Civil 3D: Expressing Pipe Slopes (2D vs 3D)

September 7, 2021 Leo Lavayen

Recently a client came to us with an issue. They were doing the math for pipe slopes and were not getting the right values.  They were using the shown slope length (3D) and the slope values in an excel sheet and the numbers did not add up. 

THE ISSUE:

When labeling Civil 3D Pipes styles have options for 2D and 3D pipe length.  The catch is the Slope Label is calculated from the 2D Length, and there is NO option to show results for the 3D value.

The math was made easy in this simple design:

  • Distance from Center to Center (2D): 100’
  • Distance from Center to Center (3D): 100.50’
  • Pipe Invert Elevation Difference: 10’
  • Pipe Slope: -10%
  • Known 2D slope, solve for 3D slope

 

THE SOLUTION: 

Create a custom pipe slope label that uses the 3D length.  The formula for Slope is simple: Rise (invert drop) over the Run (3D length).  The Slope as defined in the Civil 3D help file:

"When slope is used to refer to the slope of a pipe, it is a measure of steepness. For pipes, the slope is defined by rise (or fall) over run, where rise is the difference in elevation along a run of pipe length, measured horizontally. Slope is typically represented in percent."

The calculation is created from the Toolspace > Settings tab > Pipe collection > Label Styles > Plan Profile > right click Expressions > select New

Name used here “Slope 3D” built by dividing 3D Length by Drop Across Span, dividing it all by 100, and setting format to Grade/Slope

The Expression is simple:  ({3D Length}/{Drop Across Span})/100

Once the expression is created, it will be listed in the Text Component Editor.  Custom expressions are typically placed at the top of the list and inserted like any other field.

When used, 3D Slope value shown is calculated arcuately using the 3D pipe length for its math.

This is just another solution created by leveraging Expressions using data that Civil 3D knows but requires a little work to display in a label.

About the Author

Leo Lavayen

Civil Applications Expert<br><br>As an Applications Expert, Leo is responsible for supporting, training and implementation of software for survey and civil engineering professionals. He has more than 17 years of experience helping large and small, public and private clients in the eastern United States.

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